This invention relates to a cover for a free chlorine generating cell and, in particular, relates to a flexible elastomer cover for a De Nora type chlorine generating cell. This type of cell uses an electrolytic process for producing free chlorine gas from sodium chloride. In such a cell, carbon or metal electrodes are employed for the anode and a pool of mercury is the cathode. The terminals of the carbon or metal anodes enter the tank by passing vertically through the cover and are adjustably mounted to permit maintenance of a constant electrolytic gap. The chlorine gas is evolved at the anodes and hence it is necessary to provide a seal between the anode terminals and the cover to prevent the gas from escaping except through the discharge opening. The cover must, therefore, not only seal around the terminals of the adjustable anodic electrodes but also at the periphery of the tank. It must also remain flexible to permit electrode adjustment.
The De Nora type cell operates continuously at an elevated electrolyte temperature which may be in the order of 180.degree. to 190.degree. F. (82.22.degree. to 87.78.degree. C.) Therefore, the flexible cover is subjected to the continuous corrosive attack of hot chlorine gas on the surface thereof disposed on the inside of the tank. In addition, a high concentration of ozone is present in the region around the terminals of the anodic electrodes on the outside surface of the cover. This subjects the flexible cover to two different corrosive media simultaneously on opposite sides causing embrittlement, cracking, scaling and other types of deterioration requiring frequent replacement.
Attempts to reduce deterioration and increase the life of such cell covers has included forming the covers as a laminate of: neoprene and polyisoprene, as described in U.S. Pat. No. 2,998,374; chlorosulfinated polyethylene and polyisoprene, as disclosed in U.S. Pat. No. 3,794,577; or, natural rubber and ethylene-propylene terpolymer, as disclosed in U.S. Pat. No. 3,450,621. The laminate type cover has resulted in improved life over the all rubber covers as originally employed for these cells but further improvement in the useful life of the covers has been sought.